1. Technical Field of the Invention
The present invention relates to cosmetic or dermatological triple emulsions of the water/oil/water type comprising a non-continuous fatty phase comprising, as water/oil emulsifier, at least one block copolymer composed of a polymer block derived from a monohydroxycarboxylic acid and of a polymer block derived from an alkylglycol or from a polyalkylene glycol and a photoprotective system capable of screening out UV (UV-A and/or UV-B) radiation.
2. Description of the Prior Art
It is known that light radiation with wavelengths of between 280 nm and 400 nm makes it possible to tan the human epidermis and that radiation with wavelengths of between 280 nm and 320 nm, known under the name of UV-B radiation, causes erythemas and cutaneous burns which can be harmful to the development of a natural tan; this UV-B radiation must therefore be screened out.
It is also known that UV-A radiation with wavelengths of between 320 nm and 400 nm, which causes tanning of the skin, can induce a detrimental change in the latter, in particular in the case of sensitive skin or of skin continually exposed to solar radiation. UV-A radiation causes in particular a loss in elasticity of the skin and the appearance of wrinkles, resulting in premature ageing. It promotes the triggering of the erythemal reaction or accentuates this reaction in some subjects and can even be the source of phototoxic or photoallergic reactions. It is therefore desirable also to screen out UV-A radiation.
According to the invention, the term "photoprotective system capable of screening out UV radiation" is understood to denote generally any compound or any combination of compounds which, by mechanisms known per se of absorption and/or of reflection and/or of scattering of UV-A and/or UV-B radiation, makes it possible to prevent the said radiation from coming into contact, or at least to limit the contact, with a surface (skin, hair) on which this or these compounds have been applied. In other words, the compounds targeted by the present invention are simultaneously photoprotective organic screening agents which absorb UV radiation and inorganic (nano)pigments which scatter and/or reflect UV radiation, and their mixtures.
Numerous cosmetic and/or dermatological compositions intended for the photoprotection (UV-A and/or UV-B) of the skin have been provided to date.
These anti-sun compositions are fairly often provided in the form of an emulsion of oil-in-water type (that is to say, a cosmetically and/or dermatologically acceptable vehicle composed of a continuous aqueous dispersing phase and of a non-continuous fatty disperse phase) or water-in-oil type (aqueous phase dispersed in a continuous fatty phase) which comprises, at various concentrations, one or more lipophilic and/or hydrophilic conventional organic screening agents capable of selectively absorbing harmful UV radiation, these screening agents (and their amounts) being selected according to the desired sun protection factor (the sun protection factor (SPF) being expressed mathematically by the ratio of the irradiation time necessary to reach the erythematogenic threshold with the UV screening agent to the time necessary to reach the erythematogenic threshold without the UV screening agent). In such emulsions, the hydrophilic screening agents are present in the aqueous phase and the lipophilic screening agents are present in the fatty phase.
Anti-sun compositions in the form of an emulsion of oil-in-water or water-in-oil type can comprise inorganic pigments and/or nanopigments (that is to say, pigments for which the mean size of the primary particles generally does not exceed 100 nm) based on metal oxides and in particular on titanium oxide. They are increasingly sought after due to the fact that the latter substances, when they are used in combination with conventional UV screening agents (mainly organic compounds capable of absorbing harmful radiation), make it possible to obtain very high protection factors. These nanopigments can be present both in the aqueous phase of the emulsion and in its fatty phase.
Oil-in-water emulsions are generally better appreciated by the consumer than water-in-oil emulsions, in particular due to their pleasant feel (similar to water) and their presentation in the form of a non-greasy milk or cream; however, they also more readily lose their effectiveness with regard to UV protection as soon as they come into contact with water; this is because hydrophilic screening agents, in particular acidic screening agents, disappear in water, by bathing in the sea or in a swimming pool, under a shower or when taking part in water sports; thus, anti-sun compositions which comprise them, alone or in combination with lipophilic screening agents, no longer contribute the desired initial protection as soon as the substrate (skin or hair) on which they have been applied comes into contact with water, this loss in protection factor by removal in water of the hydrophilic screening agent being all the more marked in that the lipophilic-hydrophilic screening combination present in the composition is synergistic with regard to the sun protection factor.
It is possible to have available anti-sun compositions exhibiting improved SPFs and an improved resistance to water by employing water-in-oil emulsions. This is because a hydrophilic screening agent is more persistent towards water within a water-in-oil emulsion than within an oil-in-water emulsion. However, as was indicated above, such compositions are still not entirely satisfactory insofar as they leave, after application, a feeling of greasiness which is particularly unpleasant for the user.
Thus, the need still remains as regards being able to have available anti-sun compositions which can equally well comprise hydrophilic screening agents, lipophilic screening agents and nanopigments for which the SPF would be high, stable over time and resistant to water, whatever the hydrophilic and/or lipophilic screening agents and/or the nanopigments used, and for which the cosmetic performance would be comparable with that obtained with conventional oil/water emulsions.
Other types of emulsions, known as multiple emulsions, of the water/oil/water (W/O/W) or oil/water/oil (O/W/O) type are known in the prior art. Use is preferably made, among multiple emulsions, of emulsions with an external aqueous phase, namely W/O/W emulsions, which combine the advantages of freshness on application, contributed by the water present in the external aqueous phase, and of comfort, contributed by a relatively large amount of oil. In particular, provision has been made, in the document WO-A-94/22414, for a process for the preparation of W/O/W multiple emulsions which consists in preparing a W/O emulsion comprising a glyceryl fatty acid ester as W/O emulsifier and in dispersing this emulsion in an aqueous phase in the presence of an O/W emulsifier chosen from oxyethylenated fatty alcohols and oxyethylenated sterols.
The term "W/O emulsifier" is understood to mean, within the meaning of the present invention and in the text which follows, any compound having emulsifying properties making possible the preparation of water-in-oil emulsions.
The term "O/W emulsifier" is understood to mean, within the meaning of the present invention and in the text which follows, any compound having emulsifying properties making possible the preparation of oil-in-water emulsions.
Unfortunately, the stability of the emulsions obtained according to this document is insufficient to satisfy the requirements of commercial products, in particular on storage at high temperatures, for example greater than 40.degree. C. Such an instability can result in a W/O emulsion, resulting in a loss of the qualities of the multiple emulsion, in particular its quality of freshness on application, since the external phase is no longer an aqueous phase. This multiple emulsion can also be converted into an O/W emulsion, which is often unstable with phase separation into an oil and water. Moreover, these emulsions require a choice of specific oils in large amounts which are not very emollient and are not always well tolerated by the skin and can cause irritation.
Cosmetic W/O/W triple emulsions comprising a W/O primary emulsion comprising, in the non-continuous fatty phase, as W/O emulsifier, a polyoxyethylenated (2.5 mol of ethylene oxide) and polyoxypropylenated (1.5 mol of propylene oxide) derivative of a mixture of glycerol and sorbitol esters of hydroxystearic and isostearic acids, sold under the trade name Arlacel 780 by the Company ICI, are also known in Application EP-A-691,839.
Applicant has found that emulsions of this type could not be used in the field of the protection of the skin and hair against UV radiation, in particular against solar radiation, insofar as they were unstable on storage in the presence of hydrophilic screening agents and/or of lipophilic screening agents and/or of nanopigments based on metal oxides in their composition.